Tobacco use is the primary preventable cause of disability and death in much of the world . In the United States alone, 440,000 people die each year from smoking-induced disease, and half of all long-term smokers will die of a smoking-related disease. Smoking has a powerful dependence component[unreadable]70% of smokers say they want to quit, but more than 90% of those who try fail to do so. For most smokers, tobacco use is sustained by nicotine dependence. Current pharmacotherapies for smoking cessation are nonselective and minimally effective. The long-term objectives of the proposed application are thus to develop additional, improved pharmacotherapies. To that end, we will first test the hypotheses that the alpha3beta4 subtype of the .nicotinic acetylcholine receptor is a suitable target for nicotine medication development, and that receptor antagonists can diminish the rewarding aspects of nicotine and other drugs of abuse. Although alpha3beta4 antagonists have shown efficacy in reducing self-administration of nicotine and other drugs of abuse, no selective antagonists are known for this site. Selective and high-affinity ligands will be designed on the basis of molecular modeling studies and development of a receptor-selective pharmacophore. Molecular determinants of agonist and antagonist activity will also be explored. Compounds will be tested in vitro for binding affinities and functional activities on HEK cell lines that have been transfected with the alpha3beta4 and the alpha4beta2 nicotinic acetylcholine receptor subtypes. Lead compounds will be examined more carefully using patch clamp electrophysiological techniques to determine whether activity is voltage- or activity-dependent and to determine the rate of desensitization of the receptors. Finally, lead compounds will be tested to determine whether they attenuate nicotine self- administration in mice. Because alpha3beta4 antagonists have been claimed to block the reward induced by many drugs of abuse, lead compounds will also be tested to detemine whether they attenuate morphine and cocaine-induced place preference in mice. Tobacco use is a serious public health problem with no good pharmacotherapies for smoking cessation currently available. The novel subtype-selective nicotinic receptor ligands discovered will be useful as pharmacological probes for better understanding the role of alpha3beta4 nicotinic receptors in nicotine addiction and reward, and can be developed as potential smoking cessation medications.